Reduction of residual noxious gases in gas hardened molds and cores

ABSTRACT

A PROCESS AND APPARATUS TO PRODUCE FOUNDRY CORES AND MOLDS BY THE USE OF TOXIC AND NOXIOUS BASIC, I:E, ALKALINE, REAGENT GASES, SUCH AS AN AMINE GAS, TO CURE CERTAIN MICTURES OF SAND AND RESIN BINDERS, THE BINDERS BEING CURED BY THE REAGENT GASES TO STABILIZE THE CORES AND MOLDS. THE CORES AND MOLDS MAY ALSO, IF DESIRED, INCLUDED A COMBINATION OF TWO DIFFERENT BINDER SYSTEMS INCLUDING A RELATIVELY EXPENSIVE RESIN BINDER, ESPECIALLY TO PRODUCE PRECISE WORKING SURFACES ON FINE SAND SURFACES AND A MORE ECONOMICAL BACK-UP MASS OF COARSER SAND BONDED BY LESS EXPENSIVE BINDERS SUCH AS SODIUM SILICATE. THE NOXIOUS AND TOXIC GASES ARE REMOVED FROM THE PRODUCTS TO A SUFFICIENT DEGREE FOR TOLERANCE FROM A HEALTH AND COMFORT STANDPOINT. THIS RESULT IS ACCOMPLISHED BY USING AIR TO FORCE THE AMINE GAS INTO THE INTERIOR OF THE MOLD OR CORE AND A COMBINATION OF VACUUM ND AIR PURGING STEPS.

March 5, 1974 L. R. ZIFFERER ET AL 3,795,726.

REDUCTION OF RESIDUAL uoxxous GASES IN GAS HARDENED MOLDS AND coREsFiled Aug. 17, 1971 3 Sheets-Sheet 1 Q \-?o A|R CHAMBER LS-l CHAMBER '1l2 ATMOSPHERE 2-WAY SOL. PRESS.

VALVE S W. '0 CORE ox I l s-2 CO2 40 FILTER L ll VALVE I I I /-PRESS.

3o s w. REAGENT GAS VAQS 2-WAY SOL. VALVE ll 28 F% 2-WAY s0| VALVE 2.244 l k u I PRESS. 32 46 n sw. 22.

EFFLUENT AIR JFATMOSPHERE OR CO2 VAC. PUMP 52 CIRCUT CONTROL UNIT 0INVENTORS l v LOTHAR R-. Z IFFERER 58 LESTER F. STUMP JR.

I BY jWM AT TOR Y United States Patent 3,795,726 REDUCTION OF RESIDUALNOXIOUS GASES IN GAS HARDENED MOLDS AND CORES Lothar Robert Zilferer andLester F. Stump, Jr., York, Pa., assignors to Alphaco, Inc., York, Pa.Continuation-impart of application Ser. No. 22,586, Mar. 25, 1970. Thisapplication Aug. 17, 1971, Ser. No. 172,524

Int. Cl. B22c 9/12 US. Cl. 264-82 13 Claims ABSTRACT OF THE DISCLOSURE Aprocess and apparatus to produce foundry cores and molds by the use oftoxic and noxious basic, i.e., alkaline, reagent gases, such as an aminegas, to cure certain mixtures of sand and resin binders, the bindersbeing cured by the reagent gases to stabilize the cores and molds. Thecores and molds may also, if desired, include a combination of twodiiferent binder systems including a relatively expensive resin binder,especially to produce precise working surfaces on fine sand surfaces anda more economical back-up mass of coarser sand bonded by less ex pensivebinders such as sodium silicate. The noxious and toxic gases are removedfrom the products to a sufficient degree for tolerance from a health andcomfort standpoint. This result is accomplished by using air to forcethe amine gas into the interior of the mold or core and a combination ofvacuum and air purging steps.

This application is a continuation-in-part of Ser. No. 22,586, filedMar. 25, 1970, and now abandoned.

BACKGROUND OF THE INVENTION In general practice, sand cores and moldsare made by mixing sand with from 1% to liquid binder to obtain a freeflowing mix which is formed around a pattern in a flask or in a core boxto the desired shape. Binders, depending upon the type used, may bedried or cured to harden the sand form by heat or by the use of reagentgases. In all instances, the hardened sand forms are held together bythe cured or dried binder to provide operative working surfaces which,in the case of cores, form cavities in metal castings or, in the case ofmolds, form the outer or finished surfaces of metal castings.

It is important in founding metals that the cores which are used havecertain desired characteristics which enhance the economics of theoperation. Among these characteristics are; the necessity that thecuring process must be rapid and such as to minimize the cost of patternequipment. The core which is produced must retain its form and strengthuntil the metal stabilizes or freezes and then the core shoulddisintegrate as rapidly and completely as possible to minimize the costof removing the residual sand component of the core from the internalvoids and cavities in the casting. Other properties of a core which aredeemed necessary are that it not cause hot tears in the castings,pinhole porosity or other surface defects which Wouldsubtract fromdimensional tolerances or the physical strength of the casting, and thatthe core retain its properties in highly humid atmospheres. Cores formedby the use of resin binders excel in these properties, as compared withcores formed with conventional non-resin binders.

Many processes are used at present for the production of cores, butresulting advantages increasingly favor cores which are cured in thecore box or pattern before being removed therefrom. These are calledprecision cores and are distinguished from cores which are transferredfrom boxes into dryers for drying in ovens, which result frequently inwarping or abrading in handling. The econ omy of production and improvedquality of cured-in-thebox precision cores greatly exceeds conventionalcores and great emphasis is being put at present on methods andprocesses which can improve the production speed and minimize thepattern cost to produce such quality cores.

Prior Pats. Nos. 2,824,325; 2,876,510; 2,928,149, and 3,098,269 of oneof the instant applicants are directed to curing sand binder mixes in acore box by the use of C0 gas or other acid gases which react withsodium silicate binder and can be neutralized. In some instances, thecore box containing the sand binder mix is placed in a vacuum chamberwhile in other instances, the core box is equipped with a check vent andthe core is cured in the box without the use of a chamber. By thesemeans, acid gases are used as a reagent for the binder to produceprecision cores. The gases used as reagents were either nontoxic orcould be neutralized successfully and the various apparatuses describedin these patents were satisfactory for their intended purposes.

As this art has progressed, various resinous binders have beendiscovered to be useful which can be cured very rapidly with basic oralkaline reagent gases to produce cores that have good physicalproperties and have excellent collapsibility after the molten metal hasbeen stabilized or frozen. These two properties are in many situationssuperior to those of cores and molds produced by sand which includessodium silicate reacted with CO reagent gas as a binder. The variousresin compositions of the binders currently used require the use of NHor, preferably, one of the amine gases or vapors such as trimethylamineor triethylamine as curing agents. These gases are basic and do notinjure the internal part of vacuum pumps, automatic valves, patterns orcore boxes employed in the process and apparatus, and therefore aredesirable from this standpoint. However, these basic gases or vapors aretoxic and noxious, and it is therefore necessary that concentrationthereof in the work area be maintained below 25 parts per million of airso as to be reasonably tolerable for comfort and safety of theoperators.

To date, it has been extremely difficult to develop pattern equipment orcore boxes with seals that can dependably contain these gases while theyare pressurized to permeate completely through the sand-resin mix. Inaddition to this difliculty, the use of a mixture of air and basictriethylamine, according to presently used pressurizing methods, leavesa residue in the cured core or mold of triethylamine condensate whichslowly emanates from the core as a noxious vapor after the same has beencured and removed from the box. As a result, cores cured by suchreagents require very expensive pattern equipment and continue torelease concentrations of triethylamine into the work area to suchextent that the 25 parts per million concentration established as aminimum health standard cannot be maintained economically. The toxicityhazard and odor characteritsics of this process therefore hashandicapped its acceptance by the industry.

While 25 ppm. of trimethylamine or triethylamine are deemed adequate asa concentration to meet the minimum health standards, the realities arethat such amines are the same gases as are given off by decaying fish ormeat and are so noxious that much lower concentrations must be achievedif the processes using these reagents are to gain acceptance. As anexample, a person walking through an area with a concentration of 25ppm. of such reagent gases can absorb enough of the odor in his clothingthat it can only be removed by aerating the clothing for two or threedays in a wellventilated space. While some other amines are less noxiousthan trimethylamine and triethylamine, the difference is only a matterof degree, since all amines have this characteristic of objectionableodor.

SUMMARY OF THE INVENTION It is the principal object of the presentinvention to provide apparatus and methods which can be used to:

(a) positively assure work area concentration of noxious binder reagentsbelow objectionably detectable levels,

(b) conserve the use of costly reagents,

(c) make possible the use of simple pattern equipment which can be madefrom substantially any materials and eliminate the need for expensiveseals,

(d) greatly increase the speed of the curing process, and

(e) make possible the complete curing of large cores in large boxeswhich is not currently feasible by present pressurizing methods.

It is another object of the invention to provide a control system whichsequences positively and in a foolproof manner by means of sensing thepressures in the chamber and thus minimizes the total machine cycle timeirrespective of the size of core or mold being cured or of the size ofthe chamber employed and produces a predictable concentration level ofnoxious gases in the void spaces between the sand grains of the curedcore, the desired steps of the process occurring strictly andautomatically in an uninterruptable manner until the cycle is completedto provide mold and core products which present no health hazard and aretechnically satisfactory.

It is a further object of the invention to provide a core or moldcomposed of two different sand and binder systems to minimize theoverall cost thereof while providing maximum smoothness on the workingsurfaces with adequate strength furnished by less expensive backup sandand binder material.

Details of the foregoing objects and of the invention, as well as otherobjects thereof, are set forth in the following specification andillustrated in the accompanying drawings comprising a part thereof.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic layout of anexemplary system capable of employing the principles of the systemcomprising part of the preesnt invention.

FIG. 2 is an exemplary electrical circuit for the system shown in FIG.1.

FIG. 3 is an exemplary graph of pressures employed in a preferredcycling sequence of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For purposes of facilitatingthe comprehension of the present invention, some basic situations andcharacteristics of molds and cores with which the invention is concernedare set forth, as follows.

100 pound core requires approximately 1 cu. ft. of sand and there willbe approximately 4 cu. ft. of void space between the sand grains.Therefore, the residual concentration of gases therein at the end of thecure would be or 1 part in 80,000 or approximately 12.5 p.p.m. As thesetrapped gases which occupy void spaces in the core are given off, theyare diluted by the surrounding air and, as an example, theconcentrations in the work area will be maintained below 1 p.p.m. if the.4 cu. ft. of reagent air mix further mixes with 5 cu. ft. of ambientair. At levels below 1 p.p.m., the amine gases cease to be detectable ornoxious. As the reaction chamber is opened to atmosphere, air is used topurge it so that the chamber itself when opened has a concentration ofless than 1 p.p.m. and this concentration likewise cannot be detected.

Improvements to the vacuum gassing equipment of the aforementionedpatents which comprise part of the present invention also makes possiblethe use of the noxious reagent gases such as trimethylamine andtriethylamine with low cost wooden core boxes or conventional equipmentand completely eliminates the hazard of undesired reagent gases in thework area by the use of automatically sequencing control means' 'Furtherin accord with the invention, a number of process steps are necessary toachieve a substantially complete cure of the binder and to achieve theextremely low residuals of reagent gas in the cured product. Theseprocess steps are necessitated by the kinetics of gas movement and bythe rates of diffusion between two dissimilar gases. The followingsequence of events takes place at various stages of the process. Forpurposes of illustration, atmospheric pressure will be assumed to be 760mm. of Hg.

An exemplary core box 10 containing a cavity is filled with a sand-resinmix in which the resin may be selected from any suitable organic resinsuch as those referred to, for example, in Pats. Nos. 3,428,110, datedFeb. 18, 1969, and 3,409,579, dated Nov. 5, 1968. An appreciable rangeof such resins are referred to therein, such as epoxy, polyester,petroleum polymers, alkyd, and phenol-formaldehyde thermosetting resoleresin, which are supplemented by various additives, includingpolyisocyanate, one sepcific example of which is 4,4diphenylmethaneisocyanate. The foregoing are merely illustrative ratherthan restrictive, as long as the same may be reacted with an appropriateamine such, for example, as those referred to above, in suitableproportion to set the resin and thus solidify the sand mold or core.

In the foregoing curing procedure, the chemistry involved actually isthat the trimethylamine or triethylamine is a catalytic reagent gaswhich accelerates chemical reaction of phenolic resin binder, forexample, in one part of a suitable solvent with polyisocyanate inanother part of a solvent. Only relatively minute traces of the amine,such as less than 0.1%, by weight, of the mixture, are required for suchcatalytic purpose. The polymerization reaction of the phenol andisocyanate effects a rigid resin bond upon the sand particles which, perse, do not enter into such chemical reaction which produces the bond.This phenomenon distinguishes this process over certain prior processesin which the sand filler or aggregate engage chemically in forming thebond of the product.

The core box 10 is placed in a vacuum chamber 14. The chamber may be ofthe bell-type, raised and lowered by a cylinder and piston unit 16, orbase 18 may be raised relative to the bell 14, if desired. When thechamber is closed, the pressure therein is reduced by means of a vacuumpump 20 to approximately 12 mm. of Hg, as shown in FIG. 3. Furtherreduction in pressure is not practical as the solvent in which the resinis dissolved would vaporize. At this point, the chamber pressure is ofan atmosphere of absolute pressure.

A solenoid-operated valve 22, which preferably is actuated by apressure-responsive switch 24, is connected in conduit 26 between thevacuum chamber and the pump 20. Valve 22 is closed when saidaforementioned degree of vacuum is reached, and a solenoid-actuatedvalve 28, which is operated by another pressure-responsive switch 30, isopened to connect the vacuum chamber to a source of reagent gas insupply source 32. The exemplary tank 32 is merely illustrative of anysuitable source of reagent gas such as trimethylamine or triethylamine.

When the reagent gas enters the chamber, the atmosphere of air withinand surrounding the core box feeds into the core box ahead of thereagent gas before diffusion between the two gases can take place. It isnecessary to limit the pressurization of the chamber with such reagentgas to approximately 50 mm. of Hg absolute pressure, as also shown inFIG. 3, and this is controlled by means of the pressure-responsivecontrol switch 30 which closes valve 28. Subsequently, atmospheric airfrom inlet 34 is introduced through a 3-way valve 36 andsolenoidactuated valve 38, controlled by a further pressure-responsiveswitch 40, to bring the chamber pressure, through conduit 42, to about735 mm. of Hg. The incoming air which follows the reagent gas forces asufficient quantity thereof into the extremities of the core box andespecially into the voids within the core to at least partially cure thesame during the time within which the air is increasing the pressure tosaid exemplary pressure of about 735 mm. of Hg. Such time is adequate tocure the resin to a substantial degree but not completely.

When vacuum gassing foundry sand cores and molds to remove reagentgasses of the type employed in the present process, it has been foundthat single cycle gassing is not sufficient to produce fully curedproducts. There are occluded pockets of air in the innermost voids whichare not removed by a single evacuation and the reagent gas is precludedfrom entering such voids. Hence a second cycle of evacuation andapplications of reagent gas and atmospheric air are undertaken accordingto this invention, as follows.

The next series of steps in the process of the invention is for purposesof finally and substantially completely curing the cores in theinnermost portions and comprises again reducing the chamber pressure toapproximately 12 mm. of Hg, followed by pressurizing the chamber withreagent gas to 50 mm. of Hg, and again introducing atmospheric air tothe chamber to restore the pressure to 735 mm. of Hg to force thereagent gas ahead of the air into the innermost voids of the core toeffect curing the resin binder completely throughout the product andthereby produce a relatively rigid core having adequate strengththroughout the mass thereof. This operation also intimately mixes theresidual air and reagent gas incident to producing a fully cured core.Obviously, molds may also be made by the foregoing procedure and asubstantially fully cured mold likewise will be produced at thecompletion of said process. At this stage of the process, a reagent toair mixture of approximately 1 part in 20 is present in the chamber andin the core.

The chamber 14 is again reduced to 12 mm. of Hg by the pump 20 and, whenthat degree of negative pressure has been reached, air from inlet 34again is introduced to increase the pressure to about 735 mm. of Hg.This procedure also preferably is repeated to positively insure adequatepurging of the chamber and core or mold of the reagent gas, except thatin said repetition of such procedure the pressure is raised to 760 mm.of Hg and the chamber 14 then is opened at a controlled rate by cylinder16 while the vacuum pump 20 preferably continues to operate to remove,by scavenging, the 12.5 ppm. of reagent gas-air mixture from the chamberand thereby reduce the chamber concentration of reagent gas preferablyto less than 1 p.p.m.

While a typical and preferred embodiment of the process has been setforth when using either trirnethylamine or triethylamine as a reagentgas, it is possible that other amines would permit the elimination ofthe last stage of purging with air. The extent to which an odor isdeemed tolerable also can permit different absolute pressures intheevacuation and repressurization with the reagent gases.

The preferred steps essential to achieving an acceptable curesubstantially throughout a core or mold have been outlined above. Itshould be noted that the double repressurization of the chamber withreagent gas from 12 to 50 mm. requires of an atmosphere of reagent gasper stage or of an atmosphere per machine cycle. Such economy which isrealized in the use of reagent gas by this process is as important toits commercial acceptance as the elimination of noxious odors in thework area.

This invention also is adapted to produce a core or mold composed of twochemically cured sand systems. Inthis regard, it often is desirable totake advantage of the properties of a chemically cured organic binder inone part of a mold or core and to use another binder material, such assodium silicate, in another part. Thus, the different properties of twobinder systems can be used to best ad 6 vantage. Sometimes largequantities of a cheaper binder can be used in lieu of a more expensivebinder system.

As an example of the foregoing, a relatively thin facing of an organicbinder-sand mixture on a pattern can be backed up by a more massivesodium silicate-sand mixture. In the gassing process used to cure thebinders, an amine gas is first introduced into the chamber, afterinitial evacuation to 12 mm. of Hg, to repressurize the chamber to 50mm. of Hg, and then CO gas, rather than air, is introduced to completepressurization of the chamber to about 735 mm. and thereby force theamine gas into the voids of the core or mold being formed. This isaccomplished by an initial manual setting of 3-way valve 36 in theapparatus system shown in FIG. 1 to connect the tank 44, containing COunder pressure, to chamber 14. Such procedure is repeated and then thetwo purging stages using air, as described above, are used, whereby thechamber is re-evacuated to 12 mm. and pressurized with air which, on thefinal stage, raises the pressure to 760 mm. before opening the chamber.To accomplish this Without disturbing 3-way valve 36, asolenoid-operated valve 46, which communicates with the atmosphere andis controlled by pressure-responsive switch 48 is connected to conduit26 and is suitably controlled to effect such cycling.

In some limited situations, it may be desirable to use the sodiumsilicate-sand mixture as a facing and the organic binder-sand mixture asa back-up material to obtain the benefit of the collapsibility and lowgas evolution which characterizes the resin binder.

The ability to obtain full cures of a two binder system can contributesubstantially to the flexibility and economy of the process in certainoperations, such as described in a copending application in the name ofone of the instant applicants.

In the above-described procedures and operation of the systems thereindescribed, it is preferred that when the pump 20 evacuates the chamber14 and the molds or cores contained therein, the noxious and toxicreagent gases withdrawn therefrom may be rendered harmless andunobjectionable by passing the pump discharge into a bath 50. Said bathmay be of a neutralized nature, such as a solution of phosphoric acid,and the neutralized product then may be discharged to atmosphere throughconduit 52. Otherwise, if desired, the exhaust from the pump may beburned, such as by combining it with acetylene.

The operations of the systems described above and the cycling of thevarious switches and valves thereof can be rendered foolproof andcyclically irreversible for safety by rendering the steps of suchprocedure substantially automatic by the use of a stepping relay 54having an adequate number of stations, whereby there is no danger ofmiscycling, as by hand operation, and a safe final atmosphere is assuredat all times. The relay 54 may be contained, for example, in a controlbox 56, shown in FIG. 1. Details of the stepping relay 52 and 54 and thecircuitry connected thereto are shown in FIG. 2 in which the steppingrelay is shown in an exploded diagrammatic manner.

The electric control circuit shown in FIG. 2 in diagrammatic manneroperates the system shown in FIG. 1 to perform the procedures andfunctions described above to correctly cycle any feasible size ofchamber with any feasible size of vacuum pump and work load because eachstage of the machine cycle is brought to a predetermined desiredpressure and this pressure, whether of an increased or decreased nature,when attained, actuates the stepping relay 54. The stepping relay 54automatically cuts off the power input to the first stage of the methodafter it has attained the correct pressure and powers the second stageof the method. When the second stage reaches its predetermined pressure,the stepping relay is again automatically actuated to shift the power tothe third stage of the process, etc. In this manner, a series of stagesof the process are sequentially powered automatically until each stageof operation of the cycle of the system of FIG. 1 has been completed,after which the chamber opens automatically and the system is ready torepeat all of the stages of the process.

It is extremely important that each stage of the system of processachieves an exact predetermined absolute pressure in order for theresidual reagent gas in air, in p.p.m., to be an exact quantity at thecompletion of forming the product. Since the size of the core or moldwill vary the space occupied in the chamber and the pumping timerequired by the vacuum pump 20, it is not practical to use time as acontrol means. If this were done, the operator would be required toseparately adjust the time allotted for each stage of the process toachieve the predetermined pressure necessary for each stage. Factorssuch as the temperature and pressure of the reagent gases, variable pumpefiiciency, depending on lubricant temperature, chamber work load,binder concentration and other factors, make a time-dependent controlsystem impracticable. The method employed by the present control circuittherefore is believed to be the most practical as a control means torepetitively attain a predictable concentration of reagent gasesremaining in the work area and completed cores and molds.

It will be seen from the following description that the control systemshown in FIG. 2 can be usel substantially equally well either to cure anorganic binder-sand mix with either trimethylamine or other amine gas,or to cure a two-binder system consisting of an organic bindersand mixand a sodium silicate-sand mix such as used to make a composite core ormold by the successive introduction of an amine gas and CO gas in asingle machine cycle. Either curing method can be selected by operatingthe manually controlled 3-way valve 34 which selectively permits theintroduction therethrough of air for an organic binder-sand core, or COgas when curing a twobinder core or mold.

CONTROL CIRCUIT To initiate the process, the toggle switch 58 is closedto energize the control system and lights the indicating lamp 60 asvisible evidence the system is ready to operate. The button of startingswitch 62 then is pressed to close relay 64 and latches the same toestablish power to lines 66 and 68. The electrically operated air valve70 thereby is energized and introduces air to the air cylinder 16 toclose the chamber 14. The stepping relay 54 is actuated by means of line72 to open stepping relay contact SR8 and close stepping relay contactSR1. As the chamber closes, limit switch LS2 closes and power isestablished in line 74 and at SR1. The vacuum line valve 22 thereby isenergized to open the line to the vacuum pump which reduces the chamberpressure to approximately 12 mm. of Hg absolute pressure.

When 12 mm. of Hg pressure is attained, the contacts ofvacuum-responsive switch 24 close to energize the stepping relay againto open SR1 and close SR2. Opening SR1 de-energizes and closes thevacuum line valve 22 and the closing of SR2 energizes and opens thereagent supply valve 28 to introduce the amine gas into the chamber. Asthe chamber pressure rises from 12 mm. of Hg to about 50 mm. of Hgabsolute pressure, the contacts of pressure-responsive switch open thecircuit which deenergizes and closes the valve 28 and energizes andopens valve 38 either to atmosphere or CO Air or CO depending upon thesetting of 3-way valve 36, is introduced under pressure into the chamberto increase the absolute pressure to about 735 mm. of Hg. When thechamber pressure thus reaches 735 mm. of Hg, a second pressureresponsive switch 48 operates to de-energize the CO or atmospheric valve38 and thereby close it and also energize the stepping relay and move itto open SR2 and to close SR3. SR3, when closed, feeds through line 74 toenergize and open the vacuum valve 22 which remains open until anabsolute pressure of about 12 mm. of Hg is again attained, whereupon thevacuum valve switch 24 operates to again energize the stepping relay toopen SR3 and de-energize and close the vacuum valve 22 and also closeSR4.

Closing SR4 again introduces the reagent gas, in the manner describedabove, to again pressurize the chamber from 12 mm. of Hg to about 50 mm.of Hg, after which the pressure-responsive switch 30 operates to closethe valve 28 and open the CO or atmosphere valve 38. The secondpressure-responsive switch 48 operates at about 735 mm., slightly belowatmospheric pressure, to close the CO or atmospheric valve 38 and againenergize the stepping relay. This movement of the stepping relay opensSR4 and closes SR5. SR5 opens the vacuum valve 22 and it remains sountil the chamber pressure again reaches 12 mm. of Hg. Thevacuum-responsive switch 24 then operates to energize the stepping relayto open SR5 and close SR6. When SR5 opens the circuit, line 74 is brokenand the vacuum valve 22 is closed. SR6, when closed, causes operation ofa second valve 46 which opens to atmosphere to pressurize the chamber alimit of substantially 735 mm. of Hg. When 735 mm. of Hg pressure in thechamber is reached, the pressure-responsive switch 48 in this circuitoperates to deenergize and close the valve 46 to atmosphere and alsoenergize the stepping relay line 72 to provide impulse A. The steppingrelay thereby opens SR6 and closes SR7. It should be noted that relayCR2 is provided to prevent a feed back to SR8 when SR6 is closed.

When SR7 is closed, the vacuum valve 22 is opened to reduce the chamberpressure to about 12 mm. of Hg, at which pressure the vacuum-responsiveswitch 24 energizes the stepping relay to open SR7 and re-energize andclose both the vacuum valve 22 and SR8. SR8 energizes and closes bothCR2 contacts to energize and open the vacuum valve 22 and also energizethe time delay re lay 76. The vacuum valve 22 admits air to the chamberuntil the chamber pressure equals atmospheric pressure. The time delayrelay 76 delays the opening of CR1 until the chamber is at atmosphericpressure and then CR1 opens and closes the air valve 70. When the airvalve 70 is closed, the air cylinder 16 is operated to open the chamberto permit removal of the core or mold which has been formed therein.

As the chamber opens, limit switch LS2 also opens and disconnects themain power circuit and leaves SR8 as the only closed contact of thestepping relay. The

opening of the chamber causes the switch LS1 to be closed for momentarycontact. The time delay relay 76 instantly closes the contacts of switch24 which energizes the solenoid of the vacuum valve 22 to open it and itwill remain open for a predetermined interval to scavange any residualreagent gases which may be left in the chamber. Time delay relay 76 thenopens to de-energize the solenoid of the vacuum valve 22 and close it.The chamber is now open. Selectively, it now can be unloaded, reloadedand recycled.

The circuit as described is illustrative to indicate how the functionsof the system are performed. In practice, it is sometimes necessary toalter the trip point of the vacuum valve control switch 24 to operate ata higher pressure than 12 mm. of Hg. This may be done, for example, ifwhen curing a composite mold, the ambient temperature of the sand-bindermix is sufficiently high that water vapor is pulled from the sodiumsilicate. Under these conditions, the vacuum switch 24 can be adjustedto operate at 50 mm. of Hg, for example, instead of 12 mm. of Hg. Whenthis is done, it is necessary to repressurize the chamber with reagentgas to a higher pressure, such as about mm. of Hg instead of 50 mm. Toachieve this, the pressure switch 30 which controls the introduction ofreagent gas is set to occur at the higher pressure.

It is to be noted that, with a given system cycle, lower residualamounts of reagent gases will occur in organic binder cores than incomposite binder cores or molds. Also, when a double air flush is deemedinsufiicient, the control circuit can be extended by the use, forexample, of a IO-stage stepping relay to make possible three air flushesby repeating the functions performed by SR and SR6. Other circuits whichare equivalent also can be devised by substituting normally open valvesfor some of the normally closed valves illustrated herein or by usinglimit switches. In this sense, the circuit illustrated herein serves toshow how to achieve the functions necessary to the cycle for a givensystem different from that shown and described.

From the foregoing, it will be seen that the electrical control circuit,the various pressure responsive switches which are in the circuit, andthe control valves for forming vacuums and selectively introducingreagent gas and/or atmospheric air are all cooperating elements in asystem by which sand cores and molds which are bonded by chemicalsetting reactions of binders and reagents by the automatic cyclicalfunctioning of the system which, at least during normal intendedoperation thereof, cannot be interrupted. The processing chamber cannotbe opened until both the atmosphere therein and the reagent content ofthe product has been reduced to a safe residual content which is neitherobjectionably noxious or toxic to workmen either while making the coresor molds, or using the same in foundry operations.

Furthermore, such products are expendable and therefore, must beproduced as cheaply as possible. Thus, speed of production with minimumphysical handling and operations is essential. The process of thepresent invention, which is operable automatically in response topressures and not time, involves no physical manipulation or handlingexcept for loading and unloading the chamber, whereby operation time isminimal. Even in regard to forming large pieces in correspondingly largecham- Ibers, only enough time is consumed to effect necessary cyclingsteps of a duration adequate to achieve complete curing of the bondingagents for the sand.

Also, in regard to forming cores and molds of two chemically cured sandsystems, essentially the same apparatus is used with the exception, forexample, of providing an additional source of a second reagent gas andshifting a valve at the beginning of the process. Hence, the savings inlabor, floor space and capital investment achieved by combining twocuring processes into one constitutes an important advantage over othermethods and systems now in use.

It is also to be noted that the processes comprising the presentinvention are operable without requiring any heat to achieve curing ofthe binder materials, thereby simplifying the components of the systemin which the products are chemically rather than thermally cured.Further, curing the resin binders of the present invention with an aminecatalyst and then withdrawing the same from the cured product issuperior to neutralizing the same in the product, for example, with anacid gas because such products of neutralization are detrimental to thecore and mold by forming a gummy residue that clogs filters and destroysand internal structure of vacuum pumps.

While the invention has been described in relation to preferred usagerelating to the degree of vacuum obtained and the sequentialintroduction of reagent and flushing gases at specific pressures, otherlevels of vacuums and pressures are usable and the premixing of reagentgases or of a reagent gas with a non-reagent gas are workablealternatives includable within the scope of the method and apparatus asherein set forth.

We claim:

1. A method of substantially completely curing a molded article for usein foundry casting and comprising a mixture of sand and an organic resinbinder curable by reaction with an amine gas, said method comprising thesteps of:

(a) subjecting said article to a high degree of vacuum of predeterminedamount within a chamber,

(b) introducing an amine reagent gas into said chamber when said degreeof vacuum is reached to impregnate said article and react with and atleast partially cure said resin binder and thereby decrease said vacuuma predetermined amount appreciably less than atmospheric,

(c) introducing atmospheric air into said chamber to increase thepressure to slightly below atmospheric to force the reagent gas into thevoids of the article,

(d) again subjecting said article to a high degree of vacuum when saidforegoing pressure has been reached to withdraw the reagent gas and airmixture and thereby enhance withdrawal of occluded air from the remotevoids in said article,

(e) introducing said amine reagent gas into said chamber when saiddegree of vacuum has been reached to cause said reagent gas to penetratesaid remote voids and thereby complete the cure of said resin bindersubstantially throughout said article, so as to permit the effectivewithdrawal of a hardened sand form from the defining pattern surface,and increase the pressure to a predetermined degree less thanatmospheric,

(f) introducing air into said chamber to increase the pressure thereinto slightly below atmospheric and thereby force said reagent gas intothe innermost voids of said article to effect complete curing of saidresin binder,

(g) further subjecting said article and chamber to a high degree ofvacuum after said predetermined degree of pressure has been reached toeffect substantial withdrawal of said air and reagent gas mixture fromsaid article to establish an absolute high degree of vacuum,

(h) introducing air into said chamber when said high degree of vacuumhas been reached to increase the pressure approximately to atmosphericand thereby greatly dilute the residual reagent gas in the article, and

(i) opening said chamber when atmospheric pressure is reached to permitremoval of said article in substantially completely bonded condition,whereby rapid curing of the resin binder is effected by consumption ofonly a minimum amount of reagent gas which is commercially economicallyacceptable and results in an acceptable safe level of reagent gas in thework area.

2. The method according to claim 1 in which said steps are performedautomatically by apparatus responsive only to absolute pressures whichare attained at the end of the various steps and thereby control thenext step in the cycle of operation of the method.

3. The method according to claim 1 including the further steps prior toopening said chamber of again automatically subjecting said article andchamber to a high degree of vacuum, and subsequently theretoautomatically introducing air into said chamber after said high degreeof vacuum has been attained to increase the pressure thereinapproximately to atmospheric and thereby dilute the residual reagent gasin said article to a greater extent than the dilution previouslyeffected in said process by the preceding steps.

4. The method according to claim 1 in which said high degree of vacuumproduced in said chamber is approximately 12 mm. of Hg.

5. The method according to claim 1 in which said predetermined amount ofdecrease in vacuum in said chamber is approximately to 50 mm. of Hg.

6. The method according to claim in which said high degree of vacuum isapproximately 12 mm. of Hg.

7. The method according to claim 1 further including the step ofneutralizing the air and reagent atmospheres withdrawn from said chamberto produce a safe disposable efiiuent gas and discharging saidneutralized gases to atmosphere with approximately no noxious odorsbeing present.

8. A method of curing a molded composite article for use in foundrycasting and comprisingan outer operative surface portion formed from amixture of relatively fine sand and an organic resin binder curable byreaction with an amine gas and a backup body formed from a mixture ofsand coarser than said fine sand and sodium silicate binder, said methodcomprising the steps of:

(a) subjecting said chamber and article to a high degree of vacuum,

(b) introducing an amine reagent gas into said chamber to react with andat least partially cure said resin binder and thereby decrease saidvacuum in said chamber to a predetermined amount substantially less thanatmospheric,

(0) introducing CO into said chamber to react with and cure said sodiumsilicate binder and increase the pressure within said chamberapproximately to atmospheric while also diluting said amine reagent gaswith said C0 ((1) again subjecting said article and chamber to a highdegree of vacuum to withdraw said reagent gases and remove occluded airtrapped within the innermost pores of said article,

(e) again introducing said amine reagent gas into said chamber tofurther react with and complete the curing of said resin binder andthereby increase the pressure to a predetermined amount substantiallyless than atmospheric,

(f) again introducing CO into said chamber to complete the curing ofsaid sodium silicate and increase the pressure within said chamber to avalue approximately slightly below atmospheric,

(g) further subjecting said article and chamber to a high degree ofvacuum to purge the same of said amine reagent gas and CO and greatlyreduce the concentration thereof,

(h) introducing atmospheric air into said chamber to increase thepressure approximately to atmospheric and thereby greatly dilute theresidue of amine reagent gas and CO in said article, and

(i) opening said chamber while applying vacuum to the same to furtherremove residual amine reagent gas and CO and permit removal of saidcomposite article in completed condition and having no appreciablyobjectionable trace of the odor of said reagent gas, whereby rapidcuring of said resin binder is effected by consumption of only a minimumamount of reagent gas which is commercially economically acceptable andresults in an acceptable safe level of reagent gas in the work area.

9. The method according to claim 8 including the further steps prior toopening said chamber of again subjecting said article and chamber to ahigh degree of vacuum, and then introducing atmospheric air thereinto toincrease the pressure approximately to atmospheric and thereby purge thesame of said amine reagent gas and CO and also greatly dilute theresidue of amine reagent gas in said article to said acceptable safelevel.

10. The method according to claim 8 in which said high degree of vacuumproduced in said chamber is approximately 12 mm. of Hg and saidsubsequent decrease in said vacuum to a predetermined amount isapproximately to 50 mm. of Hg.

11. A system for curing automatically and under conditions safe to theoperators a molded core or mold for use in metal founding and comprisinga mixture of sand and organic resin binder suitable to be cured byreaction with an organic reagent amine gas in accordance with a methodof cyclical steps, said system being operable to perform the cyclicalsteps of said method automatically and comprising in combination:

(a) a chamber operable to be opened and closed relative to supportingmeans therein for a sand core or mold,

(b) conduit means connected at one end to said chamber and the other endbeing connected to a source of amine reagent gas,

(0) conduit means connected at one end to said chamber and open toatmosphere at the other end,

(d) a vacuum pump connected by conduit means to said chamber,

(e) electrically operated valve means respectively in each of saidconduit means leading to said amine reagent gas, vacuum pump andatmosphere,

(f) pressure-responsive electric switch means connected to said valvemeans to control the opertaion thereof, said switch means being operableautomatically solely in response to pressure conditions in said chamberresulting sequentially from the cyclical steps of said method, and

(g) sequentially operable electrical relay means connected to saidelectric switch means and operable stepwise solely in response todifferences in pressure within said chamber to effect the successivesteps of introducing amine reagent gas, evacuating said chamber, purgingsaid gas by introducing air into said chamber followed by additionalevacuation of said chamber, repeating said series of steps, and openingsaid chamber to remove the cured product, whereby the use ofpressure-responsive electric switch means provides foolproof safeoperation of the system against possible failure or malfunction of thevacuum pump.

12. The system according to claim 11 further including an additionalconduit connectable to a source of CO a 3-way valve in said conduitoperable selectively to permit introduction of CO or to communicate withatmospheric air to introduce it into said chamber following theintroduction of reagent gas into said chamber, and a pressure-responsiveswitch and electrically operated valve in said conduit connected to andoperated by said switch, said pressure-responsive switch being connectedto the circuit of and operable by said stepping relay.

13. The system according to claim 11 further including a neutralizingbath adapted to contain a solution operable to neutralize said noxiousorganic reagent gas, and a conduit leading from the discharge of saidvacuum pump into said neutralizing bath to transmit said noxious organicreagent gas thereinto for neutralization.

References Cited UNITED STATES PATENTS 3,590,902 7/1971 Walker et al.164--16 2,824,345 2/1958 Ziiferer 1647 2,876,510 3/1959 Zifferer 16473,209,420 10/1965 King et al. 16416 3,038,221 6/1962 Hansberg 16473,266,108 8/1966 Dunning et a1. 16412 3,528,481 9/1970 Lund 164163,556,195 1/1971 Lund 16416 JOHN H. MILLER, Primary Examiner US. Cl.X.R.

